Thread: gas mileage ???

Yes go back to stock coil packs. Make sure your tires are inflated, and change your thermostat also. i dont think any of those things will make you lose 10mpg but they will definitely hurt if they arent right.

did you use stock spark plugs?

Originally Posted by v8teezr

msd coil packs

Problem #1

If the wires you are using are ZZP, thats problem #2.

After that you might want to check your fuel filter and catback to make sure they aren't clogged.

at 188,000 miles you should prolly change the upsteam o2 sensor aswell.

Originally Posted by v8teezr

So I just bought my 98' GTP and changed the oil, the plugs and wires/msd coil packs and put a K&N in stock air box! I rebuilt tranny as well! Car is all stock other than that with 188,xxx miles and I'm only getn 11 miles to the gallon and I baby it!!! I also removed throttle body and cleaned it very well! Also cleaned maf but still only 11 mpg what else should I looking at, injectors maybe??? Should I go back to stock coil packs until I do more mods??? I know I should be getting way better mpg than this!!! Any help would be greatly appreciated!

oil change = great but doesn’t affect mileage. Unless you overfill or not use 5W-30, then you can lose about 1%.

Spark plugs = super, they can affect mpg very noticeably, fresh plugs in the stock heat range could recover 5% or more. For a stock GTP it is Autolite 606s all the way for mpg, 605s if you drive like you stole it.

Wires = again, zero effect on mpg. Wires basically either work, or they don’t.

Tranny rebuild = great but zero mpg gain, unless you switched to synthetic fluid, then maybe a 1-2% gain

TB cleaning = awesome and necessary maintenance, but zero mpg affect.

This site hates MSD coils, but many ppl run them without any issues. They are easy to change but they’re on now, why bother if you’re not misfiring. That being said, I would have advised you not to buy them. Now on the other hand MSD wires are awesome IMO.

The K&N is good, I like them a lot. However, again zero mpg gain. The whole air filter improves mpg went out with the carburetor. Will you get slightly better acceleration, probably.

MAF cleaning = nice, that could have been a part of your issue, but apparently not.

Now if you want better mpg.
#1 Replace the O2 front sensor.
#2 Replace the O2 front sensor. (yup that is how important that little sucker is for mpg)
#3 Keep your tires at 33 psi, 30 psi is crap unless you’re drag racing. I guarantee you love the better handling too, you can go higher but traction issues start to hit above about 35 psi.
#4 Clean the junk from your trunk.
#5 Avoid idling unless necessary.
#6 Check for a stock heat range thermostat, or just replace it.

Do all this without results, I’ll go into phase 2. Man I wrote a book!

Seafoam. Buy it and run it through your system.

http://www.seafoamsales.com/how-to-u...treatment.html

You checked the gas mileage and it came out to 11 or did the dic say it's 11? If its the dic make sure you are in standard measurements and not metric.